Informal and sports shoes have used a variety of constructions to provide resilience while giving the needed support to the foot. Sponge rubber soles are common, but the resilience of these is limited because of being in the form of a continuous mass of material across the entire area of the sole. This continuity of material prevents significant lateral deflection, and thus limits vertical displacement unless the sponge has so much entrained air that wear characteristics are reduced. Another expedient has been the use of transverse ribs, where the spaces between them allows more expansion to provide for vertical compression of the ribs under load. Here, again, compromise has been necessary between the hardness required for wear, and the soft resilience needed for shock absorption. Some shoes employ inclined ribs wherein the ribs bend as well as compress in order to provide a softer cushion for the feet.
Typically, these features have been incorporated in the outsole of a laminated sole construction in which a wear resistant outsole is secured to an upper structure of the shoe. The shoe upper that covers the foot can either continue under the foot, as in a moccasin construction, or it can terminate at the edge of the sole. In the latter case, the upper typically is cemented to a thin fibrous insole board when the upper is formed or lasted, and the outsole is mounted on the underside of the insole board. A soft, cushioned insole fits in the inside of the shoe on top of the insole board and is frequently removable.
Where the cleats or ribs are provided over the bottom surface of the outsole, experience has shown that this arrangement invites the accumulation of mud and other foreign material which interferes with deflection, and has the undesirable side effect of bringing dirt along with the shoe wherever it goes. Some attempts have been made to avoid the dirt dragging problem by placing the ribs on the top of the outsole adjacent the upper or the insole board.